Development of viscoelastic tubes similar to blood pump

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The purpose of this study was to fabricate viscoelastic tubes, which was anatomically identical and functionally equivalent to the natural aorta. A rotational molding workstation which was originally developed at the National University of Singapore was used for this research. First of all, we tried to fabricate aortic arch-shaped tubes by a conventional method ; a single rotational axis was employed after silicone liquid was painted onto the mold by a brush. However, it was hard to make an even thickness tube, and it was also hard to control the quality. For the next step, several trials and errors were conducted using a rotational molding workstation under various combination of rotational speeds between two axis with different painting volume, interval and times. At last, the optimal condition to develop 1mm-thickness tube was determined as follows : rotational speeds of major and minor axis were 0.02rpm and 8rpm, respectively, a weight of silicone was 20g each for three times, and painting interval was 3hours. Then, thickness deviation which was defined as a ratio between standard deviation and average thickness culd be reduced from 30% to 20%.It was well-known that natural aorta had specific mechanical properties ; increase in pressure is small for the range of less incremental volume, whereas it becomes more for the range of higher incremental volume. We have tried to fabricated multi-layr tube, however, we haven't get a favorable result. So, other trials that contained different properties from silicone was carried out. A sponge layr was sandwiched with soft and stiff silicone layrs. The compliance values of this 3-layr tube was 0.41 1/mmHg in the range of small incremental volume up tp 40%, but it was decreased to 0.36 1/mmHg for over 40%, due to a shift of major elasctic effects from outer stiff to inner soft silicon layr.Above findings were worthwhile for the further improvements of the rotational molding machine.